Shetland 500/Hobby

[wac]

I have a Shetland 500 with a 50hp four stroke mariner, also a 5hp four stroke mariner standby. When I am onboard myself she comes up to maximum revs and on the plane no bother, when 2 persons onboard outboard revs come up to within the maximum range and gets up on the plane eventually if there is no wind or tide against you. If three or four persons onboard she will not plane at all. Could anyone give me any reason why I can't get better performance

[daveinglasgow]

Hi

this coulds be many reasons but as you say you are getting the right amount of top revs this sounds like age of engine ( they all lose hp over time) or weight ballance.

As a test get more weight at the front to ballance the boat.

also test the compresion and check that it is close to what guide is i.e. within 10 %.

remember also that 4 strokes take time to get up to speed.


dave

[wac]

Hi Dave
Thanks for your reply. I have tried her with taking standby outboard and laying it in the cabin but it didn't make much difference. The outboard is a 2006 efi model and I had it serviced by a Mariner dealer so, I, assumed it was in good working order. I will get a compression test on it as you suggested.
Angus